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why would you need this, couldn't the function just iterate over the supplied list without it being expanded?
– Martin Beckett
Commented May 27, 2010 at 14:27
38

Sure, but then you would have to call it: s = sum((1, 2, 3, 4, 5)) or s = sum([1, 2, 3, 4, 5]), the *values option makes the call look like it takes a number of arguments, but they're packed up into a collection for the function code.
– Lasse V. Karlsen
Commented May 27, 2010 at 14:29
15

Here's the real benefit: you can write functions that wouldn't otherwise be possible if you need to have a variable number of arguments. For example, C's printf function, which has 1+n arguments, is tricky to write as an exercise for any beginning programmer. In Python, a beginner can write def printf(string_template, *args) and move on.
– IceArdor
Commented Nov 20, 2013 at 7:38
2

What happens if you (accidentally perhaps :p) unpack a dictionary with only one * instead of two? It seems to do something, it seems like a tuple comes out, but it is not so obvious what it is. (edit: ok I think the answer is that it just unpacks the keys, the values are discarded)
– Ben Farmer
Commented Sep 15, 2017 at 7:47
2

The last example implies that * and ** are not only doing the unpacking but also packing! See this excellent page codingame.com/playgrounds/500/…
– H.C.Chen
Commented Feb 17, 2019 at 4:06

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```
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